DESCRIPTION: Aims. Study aims are: 1) to describe the ecology of health care in physician networks of managed care plans for insured children with asthma or diabetes; and 2) to determine the associations between the out-of-network benefits and cost-sharing of health plans and children's likelihood of seeing an out-of-network physician; and 3) to determine whether quality of care and expenditures are significantly different among children seeing in-network vs. out-of-network physicians. Design. Retrospective cohort study. Population. All children with asthma (n=12,204) or diabetes (n=1,468) covered by Premera Blue Cross, Regence Blue Shield, the Medicaid program, or the Basic Health Plan in Washington state in July 1998 - June 1999. Data Sources. Health plan information, medical claims, physician participation in plan networks, American Medical Association Physician Master File, physician office survey, physician focus groups. Measures. Health plan indexes, physician participation in health plan networks; number of physicians, by specialty, that children see inside vs. outside the network; total annual expenditures; quality indicators for asthma and diabetes; characteristics of physician offices. Data Analysis. For Aim 1, descriptive, bivariate, cluster, and network analyses will be conducted to understand the ecology of care in physician networks. For Aims 2 and 3, regression models will be estimated to: a) determine the association between out-of-network benefits and cost sharing and whether children see in- vs. out-of-network physicians; and b) determine whether quality of care and expenditures are similar or different for children seeing in- vs. out-of-network physicians.